The invention relates to the heat processing or "cooking" of foodstuff materials such as grain in the formulation of human food or animal feed. Foodstuff materials are routinely heat processed to increase their food/feed value. The goal of such heat processing is to improve palatability and digestibility, and to sterilize the feed/food. In heat processing of such foodstuffs, there are three process variables. These are moisture content of the foodstuff, process temperature, and the length of time that the foodstuff is heated. The better the control over these process variables, the better and more uniform are the results achieved in the heat treating process with attendant energy savings.
A common apparatus and method of heat processing of a foodstuff includes heat processing of feed grain. This involves the injection of live steam into a mass of grain in a steam chest or conditioning chamber. The steam is discharged at essentially atmospheric pressure, limiting the operating temperature to approximately 210.degree. F. This has several disadvantages. While boilers are quite common, they can also be dangerous and require regular safety inspections; a properly licensed operator; a supply of properly treated water for steam generation; and specialized service people available to maintain the boiler. The heat transfer efficiency and rate of cooking the grain are seriously limited by the operating temperature of the steam, since they are governed in large part by the temperature differential between the heat source and the grain. Control of the equipment is for the most part manual, whereby the process is labor-intensive and the quality of the resultant product is largely operator dependent. The steam chest typically has a cross-sectional area of several square feet and a vertical gravity flow with limited means available for mixing. Temperature gradients and "channeling" of the steam can occur, to negatively affect the uniformity of the cooked grain. Start up and shut down times are energy wasting. The introduction of boiler water chemicals into the feed is an extraneous factor of unknown response in the recipient animal. In this process, the three cooking variables cannot be separated and controlled individually making the use of modern process controllers impossible.